1. Field of the Invention
The present invention relates to a portable electronic instrument such as a camera which is supplied with electric power from a battery and selectively receives different kinds of batteries, and more particularly pertains to such an electronic instrument which selectively recieves two kinds of batteries which are different from each other in their respective shape and/or output voltage.
2. Description of the Prior Art
Several kinds of dry batteries, which are different in shape or in their output characteristics e.g. the open output voltage, the current-carrying capacity or the leakage current, are available in the market for use in portable electronic instruments. For example, batteries for use in cameras include a cylindrical battery cell of the AA type with an open output voltage of 1.5 V, a button shape battery cell of the S-76 type with an open output voltage of 1.5 V, and a packaged battery cell having a package different from the AA and S-76 type batteries in shape and output characteristics. It has been a common practice that a battery which is the most favorable battery for an electronic instrument is determined and selected, upon designing of the instrument from the commercially available batteries in consideration of the operating conditions of the instrument such as the load current of the instrument, the whole weight of the instrument and the life of the battery. Hence, battery chambers of electronic instruments have been designed to accommodate only the selected kind of particular batteries. In other words, other kinds of batteries with a different shape cannot be used.
However, the battery to be used in an instrument may not necessarily be limited to a single kind but the instrument may be designed to selectively receive plural kinds of batteries. Especially, in the case where the particualar kind of battery that is most suitable for the instrument, is expensive and can not be easily obtained in ordinary stores, it will be convenient for the user if the instrument can be used with a conventional battery as a secondary battery which is inexpensive and available in the ordinary stores even if the secondary battery is inferior to the particular battery in efficiency and other properties. Such selective accommodation of different kinds of batteries will enable the user to choose the kind of battery according to a given set of circumstances.
Meanwhile, it sometimes happens that different kinds of batteries are different from each other in their shape and output voltage. However, compactness is a requisite characteristic for the design of a portable electronic instrument such as a camera and the battery chamber of the instrument should be as compact as possible even when batteries of different shapes are to be received in the chamber. Additionally, the components and circuit constants of the circuit of the instrument are generally determined such that the circuit operates in its best condition when it is supplied with electric power from the particular kind of battery. If the secondary battery has a different output voltage from that of the particular battery, the circuit must be designed to adapt for the different output voltages. Otherwise, the circuit operates badly or might be damaged. For example, if the output voltage of the secondary battery is higher than that of the particular battery, the circuit designed to operate with the output voltage of the particular battery may be destroyed by the higher supply voltage. If the output voltage of the secondary battery is lower than that of the particular battery, the circuit may operate badly or may be inoperative due to the lower voltage supply.